Decorative light strings which are connected in series are highly popular in the United States, especially during holidays in November and December. A drawback with such light strings is that they commonly include of a plurality of individual light units with bulbs which are electrically connected in series and not in parallel. The bulbs are typically incandescent bulbs having a filament formed between two leads of the bulb, the filament giving off light when a current is passed from one lead to the other, through the filament. As the bulb is used, over time, the filament will burn out, breaking the series circuit in which the bulb is arranged. This will cause the entire light string to go out unless a backup circuit path is available to bypass the failed filament. Presently, inside of the mini-light bulb, there is a backup circuit path having a shunt system arranged in parallel with the filament of each bulb. This shunt is comprised of three turns of aluminum wire with an insulating (oxide) coating. When the filament is intact, current passes through the filament because the resistance of the filament is low compared to that of the insulating material on the shunt. However, when the filament burns out, the voltage across the leads of the bulb increases to the full line potential of 120 volts AC. The actual peak voltage at 120 volts AC is approximately 170 volts. The insulating coating on the shunt wire is designed to break down at a minimum of 40 volts to provide a backup circuit path around the failed filament. However, this ‘shorting’ mechanism only works about 70% of the time. When it fails to operate, the entire series-wired light string goes out.
One solution that allows the circuit to continue to function when there is a failure as described above is taught in U.S. Pat. Nos. 6,084,357 and 6,580,182 which is issued to the same inventor herein. The solution is to provide a backup circuit path having a semiconductor shunt system arranged in parallel with the filament of each bulb. As described in the above mentioned issued patents, the semiconductor device might be a diode array or back-to-back Zener diodes. In this manner, even if a bulb burns out, breaks, or falls out of its socket, the rest of the light units in the light string remain on because the series circuit remains closed.
The system employed in the above issued patents is the shunting of each light bulb in the string with such a semiconductor shunt mounted in a package as the standard DO-41 package. The DO-41 package housing the semiconductor chip is placed inside of each socket and is electrically connected to the light bulb's conductive connection in the socket.
While the availability of decorative light strings using this type of shunt works well, there remains a need to improve shunts as set forth herein. Further, there is need to decrease the cost of producing the decorative light string.